For some time the goal in dental medicine has been to replace the classical filling material amalgam with composites (xe2x80x9cplasticsxe2x80x9d). In contrast to amalgam, it is necessary in the provision with composites to use a bonding agent. This so-called bonding is applied on the prepared hard tooth substance prior to the insertion of the composite into the cavity.
One important requirement of users of dental materials is that the processing be as simple as possible, that the processing not allow any processing errors and that the desired results are always the same.
This requirement can be fulfilled at least to some degree when single component dental materials are prepared and processed.
The use of single component dental materials assumes that the polymer-forming reaction can be initiated either by supplying energy and/or through reaction with components of xe2x80x9cactivexe2x80x9d surfaces or the surrounding atmosphere.
A typical case for the initiation of polymerization through the supply of energy is photo-induced curing of dental materials, where irradiation with light causes the decomposition of the photo initiators into polymerization initiating species.
The curing rate of such photocuring dental materials is generally very high, but curing takes place only in the areas reached by the light.
Due to the short lifespan of the polymerization initiating species, like the free radicals, it is usually only possible to realize the exposure and thus the curing at the site of the end use of the cured dental material.
This circumstance restricts the use of photocuring for dental materials. Therefore, dental materials are desired that exhibit, as single component preparations, an adequate shelf life and that can be easily xe2x80x9cactivatedxe2x80x9d.
In this respect xe2x80x9cactivabilityxe2x80x9d means that the polymerization initiating species are produced in the dental materials taken from the storage container through the introduction of energy and/or through reaction with components having xe2x80x9cactivexe2x80x9d surfaces or the surrounding atmosphere, provided that the dental materials can flow adequately freely for at least another 10 seconds following xe2x80x9cactivationxe2x80x9d in order to guarantee an application as intended.
Therefore, the object is to propose single component dental materials that exhibit stability in storage and an adequately long processing period after xe2x80x9cactivationxe2x80x9d.
The problem of the invention is solved by dental materials, containing monomers and/or prepolymers that are capable of a polymer-forming reaction; at least one initiating system, and optionally fillers, dyes, flow modifiers, stabilizers, ion-transferring substances, the x-ray opacity-increasing compounds or other modifiers, which are characterized in that the initiating system is produced in such a manner that, when brought into contact with oxygen, it releases species initiating the polymer-forming reaction; and the quantity of initiating system is dimensioned in such a manner that after bringing into contact with oxygen the dental materials can flow adequately freely and can be processed for at least another 10 seconds and thereafter cure to a solid.
The resulting smear layer is preferably less than 0.2 mg/cm2.
According to the invention, an oxygen sensitive compound is used, that when brought into contact with oxygen, can form an excited or reactive species, preferably radicals that in turn can release acid from a saline initiator by means of another reaction sequence. Said acid can initiate a polymerization reaction, in particular a cationic polymerization reaction.
This saline initiator is, for example, iodonium compounds, which, when activated, for example, by means of free radicals, can decompose into acids.
Thus, there are two initiator systems, which react with each other, to control the course of the polymerization reaction.
According to a preferred embodiment of the invention, the dental materials are taken from the sealed, oxygen-impermeable storage container and brought into contact with the ambient air within a period ranging from 1 to 120 seconds. At the same time it is expedient to provide new surfaces by filling and slightly mixing, a feature that accelerates the xe2x80x9cactivationxe2x80x9d.
According to another embodiment of the invention, the dental materials are applied on xe2x80x9cactivexe2x80x9d surfaces that release oxygen, whereby the oxygen can be produced, for example, through reaction of a compound, located on the surface, with a component of the liquid dental materials.
The dental materials, according to the invention, cure so as to form a polymer, whereby preferably such monomers or prepolymers are used that polymerize according to a cation chain mechanism, by means of a thiol-ene mechanism or according to a radical chain mechanism.
Combinations of several mechanisms are also possible.
Thus, the dental materials can contain monomers and prepolymers that cure by means of ring-opening polymerization, whereby the use of compounds containing at least two epoxide groups is preferred. Cycloaliphatic epoxide resins, which cure according to a cationic ring opening mechanism, constitute a class of monomers that can be used advantageously.
Typical representatives of these cycloaliphatic epoxide resins are described, for example, in the DE-A-196 48 283 A1.
The dental preparations, which cure according to a thiol-ene mechanism, contain multi-thiol compounds, like the tetramercaptopropionate of pentaerythritol, and multi-allyl compounds, like triallyl isocyanurate.
Such dental materials, based on thiol-ene systems, are described in detail in the DE-A 3837569, to which reference is made here.
Typical monomers or prepolymers that cure according to a radical chain mechanism and are used in dental materials are acrylates or methacrylates. Suitable are generally uni- or multi-functional (meth)acrylate monomers. Typical representatives of this class of compounds are alkyl(meth)acrylates, including cycloalkyl(meth)acrylates, aralkyl(meth)acrylates and 2-hydroxyalkyl(meth) acrylates, like hydroxypropyl methacrylate, hydroxyethylmethacrylate, isobornyl acrylate, isobornyl methacrylate, butyl glycol methacrylate, acetyl glycol methacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 2-phenylethylmethacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate and hexanedioldi(meth)acrylate, as described in the DE-A 4328960.
Long chained monomers, based on bisphenol A and glycidyl methacrylate or their derivatives, produced through the addition of isocyanates, as described in the U.S. Pat. No. 3,066,112, can also be used. Suitable are also the compounds of the type bisphenyl-A-diethyloxy(meth)acrylate and bisphenol-A-dipropyloxy(meth)acrylate.
Furthermore, the oligoethoxylated and oligopropoxylated bisphenol-A-diacrylic and dimethacrylic acid esters can be used. Quite suitable are also the diacrylic and dimethacrylic acid esters, which are mentioned in the DE-C 2816823 and belong to bis(hydroxymethyl)-tricyclo[5.2.1.02,6]-decane, and the diacrylic and dimethacrylic acid esters of the compounds of bis(hydroxymethyl)-tricyclo [5.2.1.02,6]-decane, which are extended with 1 to 3 ethylene oxide and/or propylene oxide units. This list is intended as an example and not to be understood as conclusive by any means.
Mixtures of the aforementioned monomers can also be used.
The inventive dental materials contain at least one initiating system, which upon contact with oxygen releases the species initiating the polymer-forming reaction.
Preferably the dental materials contain compounds, which are rapidly oxidized by means of oxygen, whereby free radicals are formed by this reaction or by successive reactions. Said free radicals initiate either directly the polymer formation or form, after reaction with other components of the liquid dental preparations, the species initiating the polymer-forming reactions.
Suitable classes of compounds subject to rapid oxidation by means of oxygen are, for example, substituted hydrazones and boranes.
Thus, the autoxidation of hydrazones is already described in the Report 47 (1994) pp. 3277 to 3291.
Hydrazones-containing multicomponent mixtures, which are capable of undergoing free radical polymerization by means of the addition of atmospheric oxygen, are described in the DE-A 4000776, column 2 (line 67) to column 9 (line 41), to which explicit reference is made with respect to the disclosure.
Preferably the hydrazone compounds, described in the EP-A 0510035 and in the EP-A 0594671, can also be used. These hydrazones are capable of forming hydroperoxides and are usually used as polymerization starters for monomers that are capable of undergoing free radical polymerization.
In a preferred embodiment of the present invention hydrazones of the described type are used together with iodonium compounds, in particular bisaryliodonium salts of stronger acids, to cure preparations containing epoxide group-containing monomers.
The DE-A 3041904 describes boron compounds-containing plastic compounds that cure after making contact with oxygen and that are used especially as reaction adhesives.
In the DE-A 3201780 new polymeric organoboron compounds are proposed that impart to the multicomponent mixtures, which are capable of undergoing free radical polymerization, an improved stability during high initiating action.
The EP-A 0835646 describes adhesive compositions, which contain organic boron compounds and can be used, among other things, in dental materials, like bondings.
A common feature of the aforementioned proposed solutions is that they relate exclusively to free radical curing preparations and that the important demand of users of dental materials for a preparation that is as simple as possible and for constancy of preparation results is fulfilled to a very limited degree.
The inventive preparations and processing techniques expand the possible polymer-forming reactions by the cationic ring opening polymerization and thiolene systems, thus achieving adequate shelf life and simple processibility.
In preparations, which are capable of free radical polymerization, properties extending far beyond those described in the state of the art are obtained.
With the use of monomers or prepolymers, which cure by means of a cationic ring opening polymerization, not only compounds reacting with oxygen, like hydrazones or boranes, but also the presence of compounds that decompose under the influence of radicals so as to form acids are necessary.
For this embodiment of the invention, acid formers, as described in detail in the DE-A 19736471, have proved to be especially appropriate.
Based on the total preparation, the inventive dental materials usually contain 0.1 to 10% by weight, preferably 0.2 to 5% by weight and especially preferred 0.5 to 3% by weight of initiator, and based on the total preparation, usually 90 to 99.9% by weight, preferably 95 to 99.8% by weight and especially preferred 97 to 99.5% by weight of monomers or prepolymers or their mixtures.
When this combination of compounds is used, it is also possible to cure monomer mixtures that contain substances, which are capable of undergoing only free radical or only cationic polymerization, and that contain both classes of substances.
The dental materials, according to the invention, may or may not contain fillers, dyes, flow modifiers, stabilizers, ion-transferring substances, the x-ray opacity increasing compounds, or other modifiers.
Suitable fillers are, for example, substances, described in the DE-A 19648283 (page 10, lines 48-59).
When the inventive dental materials contain fillers, they comprise:
a) preferably 0.1 to 10% by weight, in a more preferred manner 0.2 to 5% by weight and in an especially preferred manner 0.5 to 3% by weight initiator,
b) preferably 3 to 84.9% by weight, in a more preferred manner 5 to 75% by weight and in an especially preferred manner 20 to 75% by weight fillers,
c) preferably 15 to 96.9% by weight, in a more preferred manner 20 to 94.8% by weight and in an especially preferred manner 22 to 79.5% by weight monomers or prepolymers or their mixtures.
If in addition the compositions contain one or more of the aforementioned additional additives, like dyes, flow modifiers etc., they are present in quantities that are customary in the dental sector.
One special advantage of the inventive preparations and processing techniques lies in the fact that the range of the xe2x80x9cactivation timexe2x80x9d and the xe2x80x9cprocessing timexe2x80x9d is determined by the composition of the activable dental materials; and the processor can influence within specific limits the requisite xe2x80x9cprocessing timexe2x80x9d by means of the intensity with which said materials are brought into contact with oxygen or air.
The dental materials, according to the invention, are packed into suitable containers, which are preferably oxygen and light impermeable, for use according to the instructions. Suitable containers are cartridges, mixing capsules, compules, or tubes.